Partitioning in Real-lime Operating Systems

摘要

High reliability RTOS products are moving away from the dynamic process model towards static partitioning. After 30 years of the Unix model, the need for highly predictable systems, generated by the spread of software control into high integrity systems, has promoted this change to a partition based model. Using interrupts, other than the system clock, is discouraged in these systems. In a partitioning operating system, memory and very likely CPU time, is divided among statically allocated partitions in a fixed manner. Hard partitions are set up for each part of the system and each has a certain amount of fixed memory and CPU time allocated to it. These allocations last for the duration of the application and cannot be altered by any component part of the system. Within each partition there may be multiple threads or processes, (or both). Just how these threads are scheduled is job of the OS. A partition will generally support a separate namespace to enable multi-programming by mapping the program into the partition. An RTOS like LynxOS-178 is an ARINC-653 partitioning operating system that supports multiple POSIX processes and address spaces; priority scheduling; priority inheritance and priority ceilings within each partition. The LynxOS schedular and operating system are moved up into each partition, while a full ARINC-653 partitioning operating lies underneath. A similar arrangement is found in Greenhills' INTEGRITY-178B and Wind River's VxWorks 653.